Generally, image forming apparatuses are known that are connected through a network, etc. to terminal apparatuses such as personal computers (PC) and forms images (prints) from image data transmitted from the terminal apparatuses. For example, when printing image data created by a terminal apparatus, a user operates the terminal apparatus to transmit a print instruction to an image forming apparatus. The image forming apparatus received the print instruction, prints the image data from the terminal apparatus on a recording paper sheet, and discharges printed paper sheets having images formed thereon into a predetermined paper discharge tray.
The user directly looks at the paper discharge tray of the image forming apparatus to check whether the image formation is completed and the printed paper sheets have been discharged in the paper discharge tray. If paper sheets are discharged, the user takes out his/her printed paper sheets from the paper discharge tray. In this manner, when the user wants to know whether his/her printed paper sheets have been discharged in the paper discharge tray of the image forming apparatus, he/she must always or at an arbitrary timing, directly look at the paper discharge tray, and that is a cumbersome work to the user.
On the other hand, if a user forgets to take his/her printed paper sheets out of the paper discharge tray, the printed paper sheets will be left in the paper discharge tray for a long time. Therefore, if a malicious third party exists, the third party may peep at the contents of the printed paper sheets left in the tray or take them out with him/her, and that increases the risk of leakage of important information. Furthermore, if the printed paper sheets are discharged over the allowable amount of discharged paper for the paper discharge tray, an accumulation amount detecting portion detects the excess to discontinue the printing, and therefore, if the discharged paper sheets are accumulated in the tray without being taken out, the amount of the discharged paper sheets eventually exceeds the allowable amount of discharged paper for the paper discharge tray as described above and causes such a problem as a discontinuation of printing.
In this regard, a printer output bin management system described in Japanese Laid-Open Patent Publication No. 2000-044018 is known as a technology of detecting that a recording paper sheet is left in a paper discharge tray to prevent a user from forgetting to take the paper sheets out of the paper tray. In this system, a print server allocates a discharge bin and gives a user a notice of prompting a user to collect his/her discharged paper sheets when the server detects that the discharged paper sheets are left in the tray for a predetermined time or longer.
Japanese Laid-Open Patent Publication No. 2000-155506 describes an image forming apparatus including a function of synthetically printing an ID image corresponding to a user on a recording paper sheet and reading the ID image to notify the terminal of the user corresponding to the ID image that the recording paper sheet is left in the paper tray.
However, the technologies described in Japanese Laid-Open Patent Publication Nos. 2000-044018 and 2000-155506 are measures to notify a user that he/she forgets to take his/her recording paper sheet out of the tray when it is detected that his/her recording paper sheet is left in a paper discharge tray, and the technologies are not intended to prevent the recording paper sheets from being left in the tray for a long time, beforehand.